The invention relates to a method for performing a filleting cut for filleting fish, wherein the fish are conveyed tail-first in a filleting line and the filleting cut is performed along a row of wedge-shaped ray bones projecting away from a main bone stem with a wedge width increasing from ray bone to ray bone by means of a pair of circular knives which have sharp cutting edges and which cut through meat, said circular knives having drive axes which are oriented at a knife angle relative to one another and define a V-shaped arrangement of the circular knives, wherein the conveyed fish are cut by the filleting cut starting from their tail end. The invention also relates to an apparatus for performing the filleting cut according to said method, comprising a pair of circular knives which have sharp cutting edges and which cut through meat, said circular knives having drive axes which are oriented at a knife angle relative to one another and define a V-shaped arrangement of the circular knives, as well as a conveying device by which the fish are conveyed tail-first in a row and which leaves a free space in which the circular knife pair is arranged for cutting off the meat along a row of ray bones of the fish. Also provided are a circular knife pair and a circular knife configured for said pair for carrying out the method and for use in said apparatus.
Filleting cuts of the kind in question are performed in order to separate muscle meat from ray bones (spoke bones) of fish. The fish to be processed or filleted are fish from which the head has been removed and which have been at least substantially gutted. Usually there is provided on one side an apparatus for cutting the muscle meat away from ventral ray bones and on the other side an apparatus for cutting the muscle meat away from dorsal ray bones. It is important that a meat yield that is as large as possible is achieved by a filleting apparatus. In other words, as little fillet meat as possible should remain on the main bone of the fish. The achievable amount of fillet meat is substantially proportional to the cut surfaces produced. Therefore, filleting knives should be guided along as close as possible to the meat-bearing bones without any bones or fins remaining on the fillet meat. In this regard, special measures are required since the geometry of ray bones which project away from the main bone stem varies over the length of the fish. At the tail end of the fish, the wedge-shaped ray bones are relatively small and thin and to a certain extent also relatively soft, whereas towards the middle of the fish they become broader from ray bone to ray bone in terms of their wedge shape at the base next to the main bone or the main bone stem of the fish.
In order to adapt the filleting cuts to the geometry of the ray bones with regard to the fillet meat yield, according to WO 99/20115 there is provided for performing a back cut a pair of circular knives which are arranged in a V-shaped manner and the cutting gap of which is variable by essentially two measures. On the one hand, it is possible to vary the spacing of their cutting edges from a fish conveying path and also their angular position relative to one another. On the other hand, the circular knives are displaceable counter to spring means. Another known apparatus provides circular knives in a V-shaped arrangement which are displaceable counter to a spring force, wherein the circular knives are arranged in relation to a fish conveying path (filleting line) in such a way that the narrowest position of the cutting gap lies above the lower zenith of the circular knives, or the zenith located closest to the fish, in order to be able to cut off fillet meat in the most optimal manner possible in spatial terms. The known measures require special machine/apparatus elements and units as well as control measures. This is associated with adjustment work and also a maintenance and cleaning effort.